Direct force trauma
Direct force trauma, such as from motor vehicle accidents, fighting (clicking teeth), bite work, kicks from farm animals,
catching flying objects with teeth, falling, or sporting accidents (e.g. hit with a golf club or baseball bat), accounts for a marked number of dental fractures. Even without fractures, impact
trauma may lead to pulpitis (see the boxed text "Pulpitis: Another outcome of trauma").
Pulpitis: Another outcome of trauma
Abrasion and attrition
Abrasion and attrition are two other causes of tooth structure loss that can predispose teeth to fracture. Abrasion is the
mechanical wearing away of teeth caused by chewing on hard objects, while attrition is the wearing away of teeth caused by
tooth-on-tooth contact (Figure 1).
1. A complicated crown fracture of the left maxillary canine tooth in a dog (A). Also note the abrasion on the right maxillary
canine tooth (B) caused by chewing on a cage. This pattern of abrasion has been called cage chewers syndrome and can predispose
the teeth to fracture, as has happened in this case. 2A. An uncomplicated crown fracture of the right maxillary fourth premolar
tooth (carnassial tooth) in a dog. It was not known how long the tooth had been fractured. Note that there is no direct pulp
exposure. The dark area (arrow) is tertiary or reparative dentin. 2B. A dental radiograph of the fractured tooth in Figure
2A. The periapical radiolucent areas indicate endodontic disease, illustrating the need for dental radiography even when the
pulp is not exposed.
PREVENTION AND EARLY RECOGNITION
Preventing dental fractures in the first place is ideal. Proper husbandry practices such as avoiding certain hard chew objects
(e.g. nylon bones, animal bones, cow hooves, rocks) and preventing cage chewing are essential for reducing the incidence of dental
When dental fractures do occur, early recognition, correct diagnosis, and adequate treatment are necessary to prevent pain
and secondary disease and to save teeth when possible. Because early recognition is important, a conscious oral examination
should be part of every physical examination. Additionally, comprehensive anesthetized oral examinations are recommended every
12 to 18 months or if any abnormalities are noted.
Enamel, the tooth structure that covers and protects the crown (the part of the tooth above the gum line), is the hardest
substance in the body. Its composition is 96% inorganic calcium hydroxyapatite crystals and 4% water and collagen.8 The inorganic component is arranged in prisms surrounded by a collagen sheath. Enamel cannot regenerate after trauma.
Beneath the enamel is a layer of dentin that surrounds the hollow pulp chamber (root canal), which contains the pulp tissue.
Dentin and pulp can be considered the same organ. Although morphologically different, the histologic boundary is not distinct.
The pulp consists of connective, vascular, and nervous tissues along with reserve mesenchymal tissue, fibroblasts, and specialized
cells called odontoblasts. Located at the periphery of the pulp, these cells continuously produce additional dentin, called secondary dentin, as long as the pulp is vital. Odontoblasts also send cytoplasmic processes into channels located in the dentin. These channels,
called dentinal tubules, run at right angles to the complex of the dentin and pulp and the dentin and enamel.
In addition to the odontoblastic process, an ultrafiltrate of blood is in the dentinal tubule as free fluid. Because of blood
pressure gradients, there is constant outward flow of this fluid.9 The dentinal tubules in dogs are 0.9 to 2.5 µm in diameter, with 20,000 to 90,000 dentinal tubules per square millimeter
of exposed dentin. The width and number of dentin tubules depend on the distance from the pulp and the cusp of the crown.8,10
The pulp tissue in human teeth communicates with the body's vascular system through a single foramen, the apical foramen,
located at the root apex. However, in dogs and cats, an apical delta exists where the pulp enters and exits the tooth root.11 As the pulp extends through the root apex, it branches several times, like a river delta. From there, it communicates with
the periodontal ligament, periapical bone, and the vascular and lymphatic systems.